1. Field of the Invention
The present invention relates to a parallel hybrid (electric) vehicle having an engine and a motor/generator (a motor serving also as a generator), an output torque of either one or both of these engine and motor/generator being transmitted to a transmission via a torque synthesis mechanism so that a vehicular running driving force is obtained from either one or both of the engine and motor/generator.
2. Description of the Related Art
A U.S. Pat. No. 6,054,776 issued on Apr. 25, 2000 (which corresponds to a Japanese Patent Application First Publication No. Heisei 10-304513 published on Nov. 12, 1998) exemplifies a previously proposed parallel hybrid vehicle, In the disclosed parallel hybrid vehicle, the torque synthesis mechanism constituted by a differential gear mechanism (planetary gear mechanism) is used to synthesize output torques of the engine and the motor/generator and the synthesized output torque thereat is transmitted via the transmission to driven wheels of the vehicle. A method of starting the parallel hybrid vehicle disclosed in the above-described United States Patent is such as to develop a torque from the motor/generator in such a manner that a revolution speed of the motor/generator is made completely or substantially coincident with the revolution speed of the engine while a rise in the revolution speed of the engine (also called, engine speed) is suppressed. When the revolution speed of the motor/generator is made completely coincident with or made substantially coincident with the engine speed, a lock-up clutch directly couples the engine and the motor/generator without any interruption. Thereafter, unless a vehicle velocity is reduced, the vehicular driving force from only the engine or from a combination of the engine and the motor/generator is developed.